KuHL 951

PM sent

951Boost

Back @ you

badmofofosho

PM's sent to both so I can get in line behind Steve.

Skip Wolfe

PM returned.

951Boost

Injectors were sold to Steve, thanks all for the interest.

Fossil

What ohm rating are the resistors that should be used with the stock 944T DME?

951Boost

1 Ohm, 50W seem to be acceptable

porschefig

BUMP: I knew this thread existed
Looks like everyone's injectors are sold! But I'm still interested in a source for resistors for the racetronix (or any) injectors.

These:
http://www.racetronix.com/3172FM.html
have a higher "coil resistance" than these:
http://www.racetronix.com/3102FM.html
is that what's required??

Porschefile

Nope, definitely NOT! Sorry, not yelling at you. I made this mistake with my Carrera and put the #3172 Siemens 55# injectors in when it really needed the #3102's, and I'd hate to see someone make the same mistake. The #3172's have approximately 12ohms of resistance, which is MUCH more resistance than stock. I believe our stock 951 injectors are 5.5ohms resistance. Can someone confirm this? Please correct me if I'm wrong. The #3102's are listed as 2.35ohms, and it seems many low impedance injectors are roughly ~2-3ohms. 5.50ohm is definitely an odd resistance for most low impedance injectors and you need resistors to account for the other ~3ohms when going with some different aftermarket ones. I spent a lot of time speculating as to what kind of problems could be caused by having too much resistance, such as in the case of using the #3172's. All I know for sure is my Carrera still ran, but pretty F'ed up and it sure wasn't happy! Thankfully I have the proper #3102's in there now.

billindenver

http://www.fiveomotorsport.com/

Got mine there, very cheap. $250 is as I recall...is in the archives if you search for it.

Bri Bro

[QUOTE=porschefig]But I'm still interested in a source for resistors for the racetronix (or any) injectors.

DigiKey link:
http://www.digikey.com/scripts/dksea...E-ND&x=15&y=11

Ohmite P/N 825F1R0E

Geneqco

IIRC workshop manual says 3.5 to 5.5 ohms. I was told by at least a couple of suppliers that the low impedance 55s don't need resistors. Can you confirm either way? Did you use resistors in you Carrera. What's the benefit/consequence of using/not using resistors?

Porschefile

I didn't use resistors in my Carrera with the proper low impedanace #3102's, however 3.2 Carreras are a bit different. I believe their stock injectors are only ~2.4ohm resistance, which puts them right around the same resistance as the 3102's and many other aftermarket low impedance injectors. To be honest, I'm not entirely sure whether injector resistors are necessary. After being in the electronic industry for several years and studying to become an electrical engineer (nope, never finished;I'm lazy! ), personally I would use the resistors as a measure of safety. By changing components in an electrical circuit and ending up with less resistance to a current, the end result is usually increased heat in most cases. The worst result of this in our injector circuit is that it can overheat/fry the DME injector driver, in effect destroying your DME. I have searched Rennlist in the past about this, and I've seen several people post about using low impedance injectors without resistors just fine. I've seen others report frying their injector driver. I'd tend to think that as long as the car is under lower loads and not taxing the injector driver too much, the driver might be "okay" enough to get by. However, under high loads like track usage, I'd tend to think it's a pretty bad idea and likely to fry the circuit. Save yourself the trouble and just use the resistors. $5-10 or so for a coupler resistors is a small price to pay for preventing a several hundred dollar catastrophy. I've only ever used resistors w/ my 55# 3102's in my 951, so that's all I know that works from experience.

Bri Bro

Here is a post I made a while ago that looked at the reason for going with resistors:

All the injectors are driven by a single Darlington transistor and are connected in parallel. There are two wires going to the injectors to reduce voltage drop. The injector drive circuit turns on hard to set the injector solenoid, then it oscillates at a lower voltage to hold the injector open. This means the average current is less the*DC calculations, but you always will see the max current when the injector first turns on.

Resistance:
Stock == 4.5 ohms / 4 =1.225 Ohm
Other == 2.5 ohms / 4 =0.625 Ohms

Current:
(Voltage across injector is 10V due to driver loss)
Stock == 10 / 1.225 = 8.16 Amps
Other == 10 / 0.625 = 16.0 Amps

Now my cross to the driver transistor shows a max current rating of 16 amps. So, you are at the upper limit went you first turn on the injector. There also is a de-rating that should be applied for the heat generated by this transistor. At 16 amps, there is no more room for this de-rating.

So, if you run it hard, put a lot of heat into this transistor, it will be running above it max rating. If your transistor came from a good batch of transistors, they may take this. If you get a sub-normal batch, they may not.

facboy

great post!